The present invention relates to a method of manufacturing an organic-inorganic composite hybrid adsorbent by impregnating activated carbon nanopores with an oxide and a water treatment method using the same.
As the industry has developed, the emergence and production of new trace hazardous materials is steadily increasing, and thus there is a growing concern for the seriousness and risk of environmental pollution due to these hazardous materials. In environmental technology developed countries including the U.S.A., attempts have been made to make the standards for allowable residual concentrations of trace hazardous materials in the environment more rigorous and to reinforce oversight of new trace hazardous materials, including establishment of analytical methods and evaluation of risk for the same, but research into integrated control management and processing systems is insufficient in Korea. Particularly, trace hazardous materials in the effluent of industrial wastewater treatment plants frequently cause water pollution problems.
Taking into consideration the reality of Korea in which water discharged from upstream areas is used as a water source for downstream areas, control of trace hazardous materials is urgently required to ensure the good quality of water sources. Among such trace hazardous materials, trace organic materials which are recently problematic in Korea include endocrine disruptors (EDCs), including hexachlorobenzene, bisphenol A, benzene, etc.
The endocrine disruptors which are chemical materials that disturb the normal functions of endocrine systems include agrichemicals such as pesticides, including DDT; conventional organochlorine chemicals such as dioxins or PCBs (polychlorinated biphenyls); phthalate, bisphenol A, polyphenylethoxylate and so on, which are associated with materials, plasticizers or detergents for use in plastic products; and some heavy metals, etc. Unlike biogenic hormones, such endocrine disruptors do not easily decompose, are stable and remain in the environment and in vivo for several years, and may become concentrated in body fat and tissue. Exposure to environmental hormones reduces the number of sperm and causes reproductive dysfunction, mutagenesis, hermaphroditism, cancer, etc.
Methods of controlling organic and inorganic trace pollutants include chemical flocculation, biological treatment, an advanced oxidation process (AOP), a membrane separation process, adsorption, etc.
Chemical flocculation is a process of inducing flocculation by the addition of a polymeric flocculant or an inorganic salt, and the removal rate of particulate materials due to flocculation amounts to about 40% at maximum, but perchlorates or endocrine disruptors do not form condensation nuclei in a liquid phase, and thus are not removed via flocculation, which is undesirable.
Biological treatment is a process of oxidizing and reducing non-degradable materials using cometabolism of microorganisms, and mainly uses aerobic activated sludge, trickling filtration, and anaerobic sludge. Also, the main mechanism for removing perchlorates using biological treatment is known to appropriately adjust the dissolved oxygen concentration and nitrates, but the main mechanism for removing endocrine disruptors using biological treatment is reported to be based on their adsorption onto microorganisms and colloids rather than their decomposition by microorganisms, and thus the accumulation of environmental hormones in microorganisms is regarded as problematic. As endocrine materials are concentrated in the sludge, the cost required to treat such sludge is increasing.
AOP is a process of forming a hydroxyl radical (OH) which can mineralize organic materials in water or to partially decompose such materials, and is mainly exemplified by ozone oxidation, Fenton oxidation, hydrogen peroxide oxidation, photooxidation, photocatalytic degradation, etc. However, AOP is problematic because byproducts are formed in the course of oxidative decomposition and cases where the toxicity of such byproducts is higher than that of original materials are reported, and this process is unsuitable as a one-step process for actual use.
Among the various treatment methods of organic and inorganic pollutants, a combination process of adsorption and separation is recently receiving attention. The adsorption process using activated carbon is widely utilized in terms of controlling a variety of organic and inorganic pollutants, and the pretreatment process using ion exchange resins is effective at controlling cations or anions in water. Furthermore, the separation process using membranes is very effective at removing a variety of pollutants from feed water without phase change.
However, most endocrine disruptors have a very low molecular weight of about 300 Da and need a high-pressure membrane such as a nanofilration (NF) membrane or a reverse osmosis (RO) membrane to separate them using the membrane separation process alone, but the high-pressure membrane incurs high pressure loss and low membrane permeability, undesirably increasing the cost of operation.
Therefore, the separation process is mainly used in combination with a pretreatment process such as the adsorption process, and the adsorption process using activated carbon functions to adsorb a variety of organic and inorganic pollutants in addition to the trace pollutants in water, and thus requires the preparation of a selective adsorbent for pollutants having low molecular weight, and research thereto is still insufficient.
Culminating in the present invention, intensive and thorough research into methods of manufacturing organic-inorganic composite hybrid adsorbents by impregnating activated carbon nanopores with ferrihydrite, goethite, hematite or magnetite, carried out by the present inventors, resulted in the finding that the manufactured adsorbent having impregnated iron oxide may more effectively remove natural organic matter having high molecular weight as well as trace pollutants having low molecular weight in water, and may be recycled using a simpler recycling method, as compared to conventional techniques.